Proteoglycan is one of the major biological macromolecules for forming the substrate of the extracellular matrix of connective tissue, as are collagen and others. Proteoglycan was hitherto obtained by being extracted and isolated from mammal cartilage (in particular, bovine cartilage). However, ever since the occurrence of bovine spongiform encephalopathy (BSE) was reported, the use of bovine cartilage has been avoided. Thus, there has been a need for an alternative source of proteoglycan, and a production method for the alternative source. In addition, since the production cost for proteoglycan is very high due to the complexity of the existing proteoglycan extraction step and the low yield, industrial application of proteoglycan has not been fully accomplished. Thus, there has been a need for a simpler method ensuring a greater yield.
As an alternative source for proteoglycan, aquatic animal tissue is attracting attention. Therefore, there have been attempts to extract proteoglycan from cartilage of aquatic animals, such as whales and sharks. However, due to catch restrictions placed on these aquatic animals, it has been difficult to produce a large amount of proteoglycan. Moreover, the extraction and isolation of proteoglycan is complicated, and some solvents, etc., used for extraction have relatively high toxicity.
Under such circumstances, there have been attempts to extract proteoglycan from the large amount of discarded aquatic animal tissues (e.g., salmon nasal cartilage). Patent Document 1 discloses a method for producing a composition (nasal cartilage powder) containing proteoglycan from salmon nasal cartilage. In particular, since proteoglycan derived from salmon nasal cartilage is assumed to have an effect for treating or preventing inflammatory enteric diseases, demand for proteoglycan is increasing. However, the method of Patent Document 1 cannot ensure sufficiently high production efficiency; thus, the method has yet to be improved in terms of efficiency.